description:
select[k1, k2] sp
select the k1'th to the k2'th elements from the given superposition
indices start from 1, not 0
final element has index -1, 2nd last element -2, and so on.
examples:
select[2,2] split |a b c d e f g h>
|b>
select[4,7] split |a b c d e f g h>
|d> + |e> + |f> + |g>
select[2,-2] split |a b c d e f g h>
|b> + |c> + |d> + |e> + |f> + |g>
head (*) #=> select[1,1] |_self>
tail (*) #=> select[2,-1] |_self>
see also:
sselect